(1) Field of the Invention
The present invention generally relates to methods for altering and cutting circuit patterns of a printed-circuit board and a printed-circuit board, and more particularly to an altering method for altering a circuit pattern on an inner layer of a multi-layer printed-circuit board (an organic printed-circuit board, such as a glass-epoxy board and a polyimide board, and an inorganic printed-circuit board, such as a ceramic board), a cutting method for cutting a circuit pattern of a printed-circuit board, applicable to the altering method, and a printed-circuit board having an altered circuit pattern.
(2) Description of the Related Art
Conventionally, in a printed-circuit board in which a circuit pattern corresponding to electronic circuits for electronic equipment is formed, spare circuit lines, spare connecting pads, spare via-holes used to electrically connecting circuit patterns on stacked layers and the like are often additionally formed for alteration of the circuit pattern based on design changes of the electronic circuits. When the design changes of the electronic circuits have been made, a new circuit pattern can be formed using the spare circuit lines, the spare connecting pads and the spare via-holes. In addition, the circuit pattern corresponding to the original electronic circuits is cut so as to be altered into a circuit pattern corresponding to the design changed electronic circuits.
Due to the use of such printed-circuit boards, even if the design changes of the electronic circuits are made, it is not necessary to make a new printed-circuit board corresponding to the design changed electronic circuits. Thus, the printed-circuit board having the circuit pattern corresponding to the design changed circuits can be rapidly prepared.
On the other hand, in recent years, printed-circuit boards have been miniaturized by increasing the density of the circuit pattern. Thus, since forming of the spare circuit lines, the spare connecting pads and the spare via-holes prevents the density of the circuit pattern from being increased, there is a tendency to abandon formation of these spare elements.
However, in a case where a printed-circuit board from which the spare elements, such as the spare circuit lines, the spare connecting pads and the spare via-holes are omitted is used, it is difficult to alter a circuit pattern on an inner layer of the printed-circuit board when the design changes of the electronic circuits have been made.
In addition, in a case where the circuit pattern on the inner layer of the printed-circuit board is altered, the circuit pattern is generally cut. In this case, the circuit pattern on the inner layer of the printed-circuit board has to be accurately cut with consideration to a position of an adjacent circuit pattern. In particular, in a case where the circuit is cut, in a non-contacting manner, using a high energy beam, such as an electron beam or a laser beam, metal powder generated by the abrasion of material of the circuit pattern causes insulation defects. The insulation defects must be prevented.